Cleaning metal surfaces



Patented June 12, 1934 D a STA I CLEANING METALSURFACES Herbert. W. Kochs, Chicago, lll aassignor to Victor Illinois Chemicalv Works, a. corporation of No Drawing. Application November 20, 1930, Serial No. 497,081

8 Claims. (01. 87-4 The present invention relates to improvements in cleaning metal surfaces, and more particularly tinned surfaces, and to detergents suitable for such use. It will be fully understood from the following description, in which specific examples illustrating the invention are set forth.

In the patent to Howard Adler No. 1,734,706, granted November 5, 1929, it has been disclosed that the corrosive or checking action produced 10 by alkaline detergents employed in cleaning tinned surfaces, for example, tin-plated sheet metal and containers formed thereof, particularly such as are used in the handling of food products of the character of milk, cream or the like, may

be substantially prevented or inhibited by the addition to the alkaline cleanser of minor proportions of soluble chromate compounds, even under conditions involving the exposure of the tinned surface to the cleanser or detergent at temperatures of 65 to 75 C. for periods of 60 minutes or longer.

It has now been found that such checking or corrosion of tinned surfaces may be substantially completely prevented, even on exposure to the action of the detergent at higher temperatures, say from 80 C. to boiling temperatures and for great- 1y extended periods of time by the incorporation into the detergent, in addition to the soluble chromate compound, of soluble alkali metal silicates such as sodium or potassium silicate and preferably having a SiOmNazO ratio of at least 1.5 or 2:1.

The alkaline cleaning agent or detergent employed in carrying out this invention may be one of the ordinary alkaline substances used for that purpose; for example, trisodium phosphate,

soda ash, soap powder, borax, caustic alkali, or

the like, or mixtures thereof. Caustic alkalies may be present in small amounts, although it is preferred that they be not employed. The chromate compound may be any water soluble chromate or dichromate, preferably of an alkali metal such as sodium, ammonium, or potassium dichromate or chromate.

The chromate compound is present in a minor proportion relative to the alkaline substance, say from 1 to 8%. The proportion of the soluble silicate employed may likewise be widely varied, constituting a minor proportion of the solid content of the mixture and. ordinarily ranges from 3 to 12% thereof.

The mixture is employed in solution in proportions to supply the usual quantity of detergent, say from to 8 ounces of the cleaning alkaline substance per gallon of water. The silicate and chromate compounds cooperate in preventing corrosion or checking of the tinned surface.

Thus, 2 punces of trisodium phosphate per gallon of water has an appreciable checking action upon tinplate in a few minutes at a temperature of C. and substantially immediately at boiling temperatures." The addition of soluble sodium silicate, in proportions up to 10 or 12%, has no appreciable effect in delaying or inhibiting the checking action. From 3 to 5% of potassium dichromate, in the absence of the soluble silicate, completely prevents the checking action on exposure for several hours at 65 C. and up to about 1 hour at boiling temperature. On use of both soluble sodium silicate and the soluble chromate in the proportions indicated with the trisodium phosphate, on exposure of a tinned surface to the solution at boiling temperature for a period of two weeks, no sign of checking appeared, nor was there any appreciable loss in weight due to corrosion of the tinned surface.

I prefer to employ trisodium phosphate as the alkaline cleaning agent, either alone or together with soda ash in varying proportions. In preparing a powdered product for commercial purposes, I prefer to use a soluble silicate, such as sodium silicate in the form of powdered anhydrous silicate or powdered hydrated silicate. Any suitable soluble chromate may be employed, the sodium or potassium chromates or dichromates being most readily available. The proportion of soluble silicate may vary from 3 to 12% of the mixture and the soluble chromate compound in proportions ranging from 1 to 8% of the mixture. Larger proportions of the soluble silicate and chromate compounds may be employed, if desired, but are in general unnecessary.

The following examples illustrate mixtures which may be prepared in dry form for commercial purposes, and used in accordance with the present invention.

Per cent 1. Trisodium phosphate 50 Anhydrous sodium silicate 10 Sodium or potassium chromate 5 Anhydrous sodium carbonate 35 Per cent 2. Trisodium phosphate 80 Soda ash Sodium or potassium dichromate Powdered hydrated sodium silicate containing approximately 25% water 10 Additional water presentin constituents employed 2 ous solutions of alkali metal detergents upon tinned metal surfaces at temperatures of 86 C. to boiling which comprises adding to the detergent minor proportions of an alkali meta: silicate and an alkali metal chromate, the silicate being approximately 342% and the chromate 18% or the mixture.

.' 2. The method as set forth in claim 1 in which the alkali metal salt detergent is trisodium phosphate.

3. The method as set forth in claim 1 in which the silicate is sodium silicate.

4. The method as set forth in claim 1 in which the chromate is sodiurn bichromate.

5. An alkaline composition for cleansing tinned metal surfaces at temperatures of 80 C. to boiling consisting essentially of analkali metal detergent having alkaline properties, i an alkali I HERBERT W. KOCHS. 

